A preform for an IS or RIS machine has a central throughgoing passage having an upper end provided with a drop ring and a lower end that can be closed by a necking shear. When thus closed a gob of molten glass is dropped into the top of the passage and is blown down therein. A gauging device or plug fits itself to the necking shear and then blows the gob up, imparting a hollow shape to it. The preform mold is then opened up and the necking shear pivots to deposit the partially formed bottle in an adjacent final mold where it is reheated and finish blown.
It is normally essential to coat the interior of the mold with a liquid which prevents the hot glass from sticking to the normally metallic mold and assures good heat transfer. Manual application of the liquid is very difficult and impossible in densely set up modern-day machines.
This it is known to provide several spray nozzles at the upper passage end for applying the lubricant and/or mold-release agent to it. This liquid must not, however, be sprayed on the faces of the mold segments that must fit together, as it eventually will clog them and prevent the mold from closing properly. Hence it is only sprayed into the passage when the preform mold is closed again.
In the standard style of operation the preform mold is closed as or after the necking shear moves into place below it, so that when the liquid is sprayed into the upper passage end, the lower passage end is blocked. As a result the liquid mist sits on a trapped pocket of air and does not settle effectively in the mold passage. In order to be assured of wetting all of the inner preform-mold surfaces, it is therefore standard to use a large volume of the liquid, a procedure that is messy and wasteful of a valuable material.